Mass growing of seedlings is commonly done on a commercial scale in greenhouses, either for resale of seedlings as such or for subsequent replantation in sites chosen for reforestation. It is also common procedure in large-scale farming operations for crops and the like, for germinating and growing seedlings in containers till such time the seedlings are ready for replantation in the field. Invariably, the seedlings are started from seeds inserted into a growth medium and grown in a controlled atmosphere such as a greenhouse till the seedlings reach a desired size. In operations involving large numbers of seedlings, it is expedient to devise arrangements wherein the required facilities are provided in the most economical and the best way possible, at the same time ensuring that the handling and rehandling of the seedlings are curtailed to a minimum. It is common practice nowadays to have arrangements wherein several seedlings can be germinated and grown in suitable large containers which may have pot-like compartments and which can be handled and taken care of conveniently and transported easily at the time of replanting. A co-pending application entitled "Seedling Transplant Unit," Ser. No. 06/321,328 and filed on Feb. 4, 1981, describes the construction of an improved arrangement for a seedling unit, facilitating easy dislodging and removal of root lumps without damage, for transplanting purposes. The seedling unit in said co-pending application is generally in the form of a plurality of pot cells joined together in the form of a tray-like structure. The pot cells may be made of a durable quality of plastics, e.g., ABS, or polypropylene or polystyrene. Either the whole seedling unit is formed in one piece or it is made by joining individually produced pots by gluing or welding or fixing into a screen of plastic or metal. The description of the "Seedling Transplant Unit" of the above-referenced pending U.S. application (Ser. No. 06/231,328) is incorporated herein by reference.
The seedling units of the type described above are usually filled with a growth medium preferably as described in international patent application PCT/SE No. 79/00229. Examples of suitable growth media include peat, or mixtures of peat, fibers and/or mull. Seeds are placed in the pots in a known way per se. The seedling units are then placed in an appropriate stand in a greenhouse wherein the underside of the seedling unit is preferably surrounded by air. By supplying suitable quantities of water and nourishment in the presence of light, the seedlings are allowed to grow to the desired size. Subsequently, the seedling units are transported out into the field or a reforestation area where the seedlings are separated and planted individually. The emptied seedling units are then returned to the greenhouse for re-use.
Statistically, a certain percentage of seeds in every batch does not sprout in time to become seedlings, or, they do not sprout at all. There may be some seedlings which start normally, but dry up too soon either because of malnourishment or because of physical damage. Such occurrences are conceivable because, in large-scale seedling operations, feeding of water and nourishment to the trays is usually mechanized, and, a slight misalignment of the feeding or watering mechanism with respect to the trays or the seedling units could result in some seedlings being missed out and/or damaged. There are yet other seedlings which start normally, but are located physically off-center in their respective pots. Such seedlings face the danger of not surviving when transplanted permanently, because of either ill developed roots which cannot support a healthy seedling, or because of the roots undergoing transplant shock owing to their eccentrically being located in the root lump and consequently not having had sufficient protection from the growth medium.
There are also several pots in every batch of seedlings wherein the seeds do not germinate at all; besides such nongerminating pots wasting the water and nourishment facilities in the greenhouse, they additionally create the necessity of having to deliberately sort them out so as to isolate them before the trays are sent out for field transplantation. If such presorting is not done, and if transplantation in the field is done mechanically, the lump of growth medium that is taken out of a nongerminated pot would be wastefully transplanted at an assigned spot which could have been occupied by a healthy seedling; or, if the transplantation in the field is done manually, the chances are that a nongerminated pot in the tray will be left untouched with its hardened growth medium. When the seedling tray is eventually returned to the greenhouse for re-use, the nongerminated pots will have to be necessarily emptied preferably manually before the trays can again be filled with fresh growth medium before seeding.
While the problems caused by seedlings that have grown completely off center in a pot can be tackled and resolved in a relatively simple manner, the matter of nongerminating seeds poses problems which require serious consideration. The costs incurred in the greenhouse maintenance and upkeep which comprise labor, cost of running the mechanized equipment, cost of plant food as well as the cost of the growth medium have to be applied to only the seedling that can be turned out with success; a large percentage of nongerminating seeds in pots, and a significant reject rate in seedlings either because they are too much off center or because they have prematurely dried would drive up the total operating costs and would result in a very uneconomical use of the greenhouse facilities. The problem of seeds not germinating at all totally, has been partly solved by inserting more than one seed in a pot, say two seeds. The germinating rate of seed depends among other things on the quality of the seeds, the plant species and to some extent on the external conditions. For some known species of trees, the germination rate is so notoriously poor that drop out of up to 40% is not uncommon. However, even though the probablity of positively having a seedling in each pot is increased by inserting more than one seed in each pot, there will be several pots where more than one seedling will result. At some stage of seedling growth in the greenhouse, or as a last resort in the field during transplantation, multiple seedlings will have to be separated from the pots which are sorted out. This again results in more manual intervention and higher costs.
The invention also teaches a method of preparing seedling trays wherein root-lumps of nonsuccessful seedlings are ejected after the unsuccessful seedling is sensed by the sensor bridge. Besides savings in the supplied nutrients, one other significant advantage of identifying and evacuating nonsuccessful pot cells is that the handling of the trays will be made relatively easier and more economical since, lifting some waste, dead weight of the root-lumps of nonsuccessful seedlings is obviated.
There has therefore been a need for obviating the foregoing problems to result in profitably exploiting the expensive space and resources available in greenhouses for mass-scale commercial growing of seedlings. It is important to ensure that as few pots as possible are rejects or vacant, at a juncture as soon as possible after the germinating of the seeds. The present invention provides an apparatus which enables optimally the best possible utilization of the greenhouse facilities with minimal waste and the maximum number of acceptable seedlings, regardless of the plant species or the quality of the seeds. The apparatus of this invention reduces the need for manual intervention in mass growing of seedlings to a minimum, thereby resulting in increased economy. By the present invention in elevated mass growing of seedlings, as soon as possible after the germination of seeds, the trays are scanned to identify the pot locations not containing an acceptable seedling; in the exact desired locations healthy seedlings together with their root lumps may be automatically placed after first emptying the pots of the old growth medium in which the seeds did not germinate. The diagnosis of the pots to be gone through to replace the faulty seedlings is done automatically too, according to the present invention. In an exemplary embodiment of the invention which uses conveyors, the seedling trays according to the pending U.S. application Ser. No. 06/231,328 filed on Feb. 4, 1981, referred to supra, by virtue of each seedling pot comprising a plurality of finger-like openings depending from the pot top opening, it is expedient to empty the contents of a pot by displacing the contents downwards; it is equally expedient to insert a replacement seedling along with its root lump, by insertion from the top. Expediently, while inserting a healthy seedling into an identified spot in a segment tray, a hollow plunger, using controlled vacuum at the top, may be used. The vacuum gently sucks the leaves of the seedling upwards to prevent damage when the root lump is discharged downwards. Other methods of evacuation of pots and inserting replacement seedlings are within the purview of this invention and can be detailed as the constructional features of the seedling unit dictate.